Electrical power lines often run through heavily wooded areas, either in neighborhoods or in rural areas. Normally a path, or right of way, is cut through such wooded areas to make way for the power lines, but eventually the trees or other vegetation will encroach upon this path and it will need to be trimmed back. For example, tree limbs over time may grow over the power lines, presenting the risk of damaging the lines should the limbs fall. Typically, such trimming is required every five years or so, although this time period can be shorter or longer in a given area. Because power lines often span long distances, such as hundreds of miles, a trimming operation can be quite a complex and time intensive endeavor for which efficiency is a priority.
Many different ways of trimming such trees in such an application have been proposed in the prior art. In one approach, a mobile unit such as a “bucket truck” is deployed. The bucket truck is so called because it has a bucket connected to a boom (a crane-like structure), which is in turn connected to the chassis of the truck. The bucket (or “gondola” as it is sometimes known) contains room for a worker and associated tree trimming equipment, such as a hand operated chain saw. Once in the bucket, the worker is hoisted up to an appropriate height to trim the trees. Thus, the worker can manually cut the tree limbs to combat encroachment of the trees toward the power lines. This approach, however, is not optimal because it is slow, and involves potential liability costs associated with hoisting a person to potentially dangerous heights while simultaneously operating dangerous equipment.
In another approach disclosed in U.S. Pat. No. 4,269,241 (the '241 patent), which is incorporated herein by reference in its entirety, the bucket on the end of the boom is replaced with a limb grasping and cutting assembly. The assembly contains jaws for clamping a tree limb to be cut, and a circular saw blade for cutting the grasped limb. The assembly can spin around the axis formed by the boom to allow the jaws to be brought into alignment with a particular tree branch. Once the tree limb is grasped, the circular saw blade is advanced away from the assembly and from the boom toward the intersection of the jaws, thereby cutting the limb. After cutting, the saw blade is retracted back inside its housing, and, in theory, the cut tree limb will be held by the jaws, which will allow the boom operator to place it appropriately on the ground for disposal. This automated process is an improvement over more manual techniques.
In another approach, disclosed in U.S. Pat. No. 5,501,257 (the '257 patent), which is incorporated herein by reference in its entirety, a similarly functioning boom-mountable assembly is disclosed for grasping and cutting tree limbs. The assembly of the '257 patent differs from that of the '241 patent in that it offers more degrees of freedom in the movement of the assembly. For example, the assembly can be pivoted away from the long axis of the boom, allowing the assembly to be bent upwards or downwards relative to the long axis, or from left to right, depending on the angle that the assembly has been rotated around the long axis. Moreover, the cutting assembly has a linear array of saws that can be swiveled through 360 degrees to provide for more flexible cutting. This automated process is also an improvement over more manual techniques.
Other prior art tree trimming apparatuses are manufactured by Jarraff Industries, Inc., Timberland Equipment Ltd., TSE International, Inc., and Kershaw, which are known to disclose similar single or multiple saw blade assemblies mounted on booms.
Still other techniques, or related techniques, are disclosed in the following U.S. patents, which are all incorporated herein by reference: U.S. Pat. Nos. 4,522,239; 4,569,379; 5,378,852; 5,390,715; 5,441,090; 776,743; 1,364,432; 2,538,371; 3,234,976; 3,343,575; 3,565,372; 3,664,391; 3,688,816; 3,720,246; 4,063,359; 3,183,949; 3,389,728; 3,529,642; 3,675,691; 3,720,246; 3,763,905; 3,974,866; 3,991,799; 4,050,488; 3,252,487; 3,443,611; 3,461,928; 3,468,352; and 2,663,952.
Another prior art practice relating to tree clearance at electrical power line right of ways deals with the administration of herbicides or wound dressing to impede tree growth. Herbicides can be liberally sprayed usually manually in the location of unwanted tree limbs or vegetation, but this approach can be undesirable and inadvertently might kill trees or vegetation that do not presently pose a problem. Additionally, providing even and controlled coverage is a problem, because the operator usually sprays the herbicide from the ground using an attachment which may need to reach heights of tens of feet and which may be difficult to manually control. Accordingly, instead of broadly spraying herbicides in the general location of trees or other vegetation encroaching on the right of way, it is preferable to administer herbicides more precisely near the edges where tree limbs have been cut. By spraying only the exposed cut portions of the trees, the herbicide or wound dressing is made more effective as it can directly enter the tree at the cut site, perhaps impeding the growth of limbs without killing the trees outright.
Accordingly, it has been known to place a worker in a bucket in a bucket truck to cut limbs and/or to hand spray herbicides on the cut portions or other limbs of the trees. This normally requires the worker to have a reservoir of herbicide in the bucket, or for the herbicide to be pumped from a reservoir on the truck itself. The worker must also usually have a manually operated saw in the bucket, as there may be locations along the right of way for which it would be undesirable or improper to spray herbicide (e.g., near a private residence having sensitive vegetation). This approach is thus inefficient. It requires first that the tree limbs be cut manually and/or sprayed manually. Furthermore, this approach again presents the problem of having a worker in the air, with its associated costs as discussed above. The worker is also subject to additional health risks, as he might become covered by the herbicide, or may be electrically shocked when spraying wet chemicals near to the power lines. Moreover, herbicide administration is potentially unfocused in its administration. Additionally, if a tree trimming vehicle such as those discussed earlier are used to cut certain tree limbs, two pieces of equipment will be needed (the tree trimming vehicle and the spray truck), which increases the costs of operation.
The art would therefore benefit from an improved, more automated way for trimming trees near power lines and for chemically treating them if necessary. This disclosure presents such a solution.